The present invention relates to video signal processing, and more particularly to depth-based recursive video effects that use depth information inherent in a three dimensional video effects digital picture manipulator (DPM) to automatically transition between over and under trails modes.
Recursive effects use a digital memory to store an image from previous frames of a video signal in order to create a decaying after-image. The video signal and associated key, or opacity, signal for previous frames are recursively decayed and combined with the incoming video signal to create such effects as "over trails" and "under trails". In over trails the incoming image appears over, or in front of, the previous image in the recursive memory. In under trails the incoming image appears under, or in back of, the previous image in recursive memory and is not seen unless the incoming image moves from beneath the stored image or there is some transparency in the stored image, such as from decay of the stored image.
The combining equations for video and key signals for over trails is: EQU V'.sub.OUT =V'.sub.1 +(1-K.sub.1).times.Q.times.V'.sub.R EQU K.sub.OUT =K.sub.1 +(1-K.sub.1).times.Q.times.K.sub.R
where K.sub.1 and K.sub.R are the incoming and stored key signals respectively, V'.sub.1 and V'.sub.R are the incoming and stored shaped video signals respectively, and Q is a frame-to-frame persistence value between zero and one where zero causes immediate decay and one causes no decay. For under trails the corresponding equations are: EQU V'.sub.OUT =V.sub.1 .times.(1-Q.times.K.sub.R)+Q.times.V'.sub.R EQU K.sub.OUT =K.sub.1 .times.(1-Q.times.K.sub.R)+Q.times.K.sub.R
The above equations are special cases of the following priority combiner equations: EQU V'.sub.OUT =V'.sub.1 .times.(1-(1-P).times.Q.times.K.sub.R)+(1-K.sub.1 .times.P).times.Q.times.V'.sub.R EQU K.sub.OUT =K.sub.1 .times.(1-(1-P).times.Q.times.K.sub.R)+(1-K.sub.1 .times.P).times.Q.times.K.sub.R
between the incoming shaped video and key signals V'.sub.1, K.sub.1 and the decayed and stored shaped video and key signals Q.times.V'.sub.R, Q.times.K.sub.R, where P is a priority control signal value of the incoming image over the stored image. When P=1, the over trails case, the incoming image has priority over the stored image, and when P=0, the under trails case, the stored image has priority, reducing the equations to the special cases above.
By using a priority combiner, such as that disclosed in U.S. Pat. No. 4,851,912 issued Jul. 25, 1989 to Richard A. Jackson and Kevin D. Windrem entitled "Apparatus for Combining Video Signals", intermediate priority levels may be achieved and there is some transparency in the image having priority. In current commercial recursive video effects, the over and under trails are modes specifically selected by the operator based on explicit front panel control. The under and over trails modes may be used to give a feeling of "depth" to the video effect in that the image having priority appears to be closer to the viewer than the image being overwritten.
What is desired are depth-based recursive video effects that use depth information inherent in a three-dimensional DPM unit to automatically transition on a pixel by pixel basis between over and under trails modes.